Field of the Disclosure
The present disclosure generally relates to a telemetry operated cementing plug release system.
Description of the Related Art
A wellbore is formed to access hydrocarbon bearing formations, e.g. crude oil and/or natural gas, by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a tubular string, such as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, and/or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annulus is thus formed between the string of casing and the formation. The casing string is cemented into the wellbore by circulating cement into the annulus defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing or liner in a wellbore. In this respect, the well is drilled to a first designated depth with a drill bit on a drill string. The drill string is removed. A first string of casing is then run into the wellbore and set in the drilled out portion of the wellbore, and cement is circulated into the annulus behind the casing string. Next, the well is drilled to a second designated depth, and a second string of casing or liner, is run into the drilled out portion of the wellbore. If the second string is a liner string, the liner is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The liner string may then be hung off of the existing casing. The second casing or liner string is then cemented. This process is typically repeated with additional casing or liner strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing/liner of an ever-decreasing diameter.
During a cementing operation for a liner or subsea casing string, the casing/liner is deployed into the wellbore at the end of a work string. The work string includes a wiper plug at a lower end thereof. The process of releasing the wiper plug downhole is typically accomplished by pumping a dart down the work string. The dart is pumped downward by injecting cement slurry or other desired circulating fluid into the wellbore under pressure. The fluid forces the dart downward into the wellbore until it contacts a seat in the wiper plug. The dart sealingly lands into the wiper plug. Hydraulic pressure from the injected fluid ultimately causes a releasable connection between the wiper plug and work string to release, thereby allowing the dart and the wiper plug to be pumped downhole as a single plug. This consolidated wiper plug separates the fluid above the plug from fluid below the plug.
A variety of mechanisms have been employed to retain and subsequently release wiper plugs. Many of these utilize a sliding sleeve that is held in place by a shearable device. When the dart lands in the sliding sleeve, the shearable device is sheared and the sleeve moves down, allowing the plug to release. Certain disadvantages exist with the use of these release mechanisms. For example, during well completion operations, the release mechanism is subjected to various stresses which may cause premature release of the wiper plug. In some situations the sliding sleeve is subjected to an impact load by a ball or other device as it passes through the inside of the plug. In other situations, a pressure wave may impact the releasable mechanism. In either of these situations, it is possible for the sliding sleeve to shear and to thereby inadvertently or prematurely release the wiper plug.